Problem: Before the previous stop there were 52 people riding on a train. 48 people ended up getting off at the stop. How many people are riding the train now?
Explanation: The number riding the train now is the difference between the number who were riding and the number who got off at the previous stop. The difference is $52 - 48$ people on the train. $52 - 48 = 4$ people are on the train.